The present invention relates to a phase detector, for measuring the phase difference between two alternating current (hereinafter abbreviated to AC) signals, and for producing an output signal indicative of the value of that phase difference. More specifically, the present invention relates to a phase detector which will provide an output signal representing the phase difference between two AC signals, which varies in a smooth and continuous over the entire measurement range, i.e. over a range of phase difference coverings 360.degree., and which will precisely and accurately indicate phase differences in the region of 0.degree..
Various types of circuit have been proposed and utilized in the prior art for detecting and measuring the phase difference between a pair of AC signals. However it has proven difficult to provide simple and effective means for ensuring that accurate phase difference will be carried out for phase differences in the region of 0.degree.. This is due to the fact that a phase difference of 0.degree. is equivalent to a phase difference of 360.degree., so that if, for example, such a prior art phase detector produces an output signal in the form of a voltage whose level varies in proportion to the phase difference between two AC signals, then this voltage will increase to a maximum value as the phase difference approaches 360.degree., and then must immediately return to a minimum value when the phase difference reaches and exceeds 360.degree., i.e. returns to 0.degree.. This requirement for a step discontinuity in the output signal from such a prior art phase detector results in a jitter or "hunting" effect when the phase difference approaches a value in the region of 0.degree. (i.e. 360.degree.), which results in detection insensitivity and inaccuracy within that region.
For this reason, although it has been found possible in the prior art to produce phase detectors which are simple in configuration and substantially accurate over most of the range of phase difference measurement, such phase detectors have the defect of having a region of insensitivity in the region of 0.degree. phase difference. This disadvantage is overcome with a phase detector according to the present invention, which will provide a smoothly and continuously varying output signal over the complete 360.degree. phase difference measurement range, without a region of hunting and insensitivity close to a phase difference of 0.degree..